Pilot reported not being able to receive clearance through PDC and requested verbal clearance from ATC. Pilot stated a portion of the clearance was not familiar to them and had difficulty getting ATC to clarify it.

Narrative

Operating Aircraft X on Day. JFK to ZZZ. Local time XA30. I was the Captain. This report relates our experience attempting to get an ATC enroute clearance while still at the gate. Our aircraft did not have PDC capability; thus we were required to contact Clearance Delivery via voice. Our attempt to get the ATC clearance resulted in considerable confusion and frustration. The controller told us simply 'you are cleared JFK TO ZZZ via the Sierra Alpha route'. Simply that. Both the FO (First Officer) and I had no idea what the 'Sierra Alpha route' was. We paused to examine both our flight plan and the JFK company pages for clues as to what the Sierra Alpha route is. After several moments of futile effort; and with departure time upon us; we considered contacting Dispatch. Instead I thought querying the clearance Delivery Controller would be faster. The Controller responded with 'it's in your WSI application'. With that information we examined the WSI app to discover numerous route options beyond the one we actually were filed for; including one that indicated 'SA' in the body of the route. I have never; ever; received a clearance in such a fashion and was not convinced that we were looking at the actual ATC clearance; since; again; we were looking at the WSI weather app. We transcribed the route; but did not load it; yet. Seeking clarification; and without a SID; squawk; or altitude; I contacted the controller again. I indicated to him that we'd found what we 'think might be' our route in the WSI app; but wished to do a full route read back and obtain altitude; SID; and squawk. I am not sure if his reply was intended to be humorous; but he replied 'yeah; it's amazing what you can find on the internet'. This struck me as sarcastic and unprofessional. I also listened in as the controller appeared to voice his weariness with other aircraft trying to get information with similar snippets of sarcasm. We finally did nail down the full clearance; but the process introduced confusion; frustration; and irritation. None of it necessary. Is obtaining the clearance via the WSI weather app a new; FAA approved method for obtaining enroute clearances? This was a first for me and the FO. A simple old-fashioned enroute clearance delivered by radio and read back by the crew would have alleviated the frustration; saved time; and most importantly; been much safer. There can be no doubt as to the precision of the ATC enroute clearance; ever; and especially in airspace as challenging as New York. This controller surely has been around awhile and understands the traditional procedure for providing an enroute clearance with subsequent read back by the crew. Because we were not the only crew seeking clarification; he is surely aware that other crews were confused. His 'Amazing what you can find on the internet' comment; in my opinion; reflected both his awareness that we were confused; as well as being interpreted as sarcastic. It was like pulling teeth to get the clearance. Unnecessary and unprofessional. If we have a new way of obtaining enroute clearances that involve researching the WSI app; then this should be reflected in a bulletin; a NOTAM; or explained by the controller at the outset.